Method and apparatus for manufacturing a cylindrical container

ABSTRACT

A new and improved process for manufacturing a cylindrical container is disclosed herein. A drawing and ironing process is used to produce a more efficient container. This process eliminates the need for a part, thereby making the process more efficient and cost-effective.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention pertains to an improved method of producing a cylindricalcontainer, and more particularly to utilizing a drawing and ironingprocess to make the container.

2. Description of the Related Art

Conventional pressure vessels, such as those used in the filterindustry, are typically “drawn” vessels or containers. Drawing is aknown metal fabrication technique wherein a given blank of material,particularly metal as used in pressure vessels, is reformed or reshapedto a particular, desired configuration. Drawing effectively retains ormaintains the virgin, or original, material thickness throughout thewalls of the vessel. Any reduction or thickening of material occurs byaccident, or within the basic tolerance of established drawingtechniques, which effect a maximum reduction of less than ten percent ofthe material thickness, more typically in the range of five to sixpercent. Variation in material thickness may also occur due toclearances within the dies employed in the drawing process. In somecases, die clearances are designed to create localized stretching in thematerial. Stretching, during a drawing operation, does not, however,impart any improved or advantageous properties to the stretched portionof the drawn metal product.

Nevertheless, drawing is an established and extensively used techniquefor the formation of pressure vessels, since it does permit formation ofa pressure vessel of, typically, cylindrical configuration and having aclosed end, without the use of seams. For example, earlier techniqueswould employ a flat sheet rolled into a container, requiring theformation of a side seam, with the further addition of an end piecesuitably seamed to the open end of the cylindrical structure. Drawingthus eliminates the side seam and the end seam of such earlier prior artpressure vessels. While affording these advantages, drawing imposeslimitations as discussed above, and moreover fails to provide thecapability of precisely sizing the vessel, not only as to its principaldimensions and particular diameter, but also, and to some extent morecritically, as to the cross-sectional thickness of the walls of themetal vessel; in drawing operations, the latter is solely dependent uponthe original or virgin material thickness. In view of the inability ofdrawing processes to size or control the material cross-sectionalthickness, it is necessary, in the fabrication of drawn pressurevessels, to select a virgin material having a minimum thickness in lightof its thickness tolerance, which is of sufficient strength to meet themaximum requirements of a pressure vessel, and to employ that samethickness throughout the entire vessel structure.

There is known in the art a fabrication technique termed “ironing,”whereby metal is physically thinned by surface extension. U.S. Pat. No.3,733,881 issued May 22, 1973 to Donald C. Grigorenko discloses a methodand apparatus for making deep drawn and ironed metal shells wherein ametal disc is subjected to both drawing and ironing operations. In theparticular process disclosed in that patent, a flat metal blank ofvirgin material is subjected to a reverse draw operation whereby theblank is shaped into a cup, or shell, of a first diameter and then isredrawn in an opposite direction to form a narrower diameter cup, orshell, of elongated axial length. The elongated shell is then subjectedto successive ironing stages to reduce the side-wall thickness and thuselongate the axial dimension of the shell. The ironing technique isknown to improve the physical characteristics of the ironed material inthe side-walls. The conventional drawing and ironing process, however,has been used heretofore primarily for realizing material reduction,i.e., reducing the amount of material required to form a vessel of agiven size, along with the elimination of the side and end seams asheretofore achieved by drawing operations alone.

The present invention comprises an improved cylindrical container havingselectively controlled wall thicknesses, so as to provide theappropriate material thickness in those portions of the vessel, asrequired for necessary “pressure” performance, yet having ironedside-walls which are of reduced thickness throughout a substantialportion of the axial extent of the cylinder.

Typically, to form a cylindrical vessel, a disc of the virgin metal iscut. The disc is then drawn into a cup-shape, which preferably may beaccomplished by the reverse drawing operation disclosed in the abovecited U.S. Pat. No. 3,733,881. The resultant, drawn, elongated shell isthen subjected to one or more stages of ironing, performed by aspecially configured mandrel which advances the drawn, elongated shellthrough one or more stages of ironing rings. The mandrel may be employedas well in the final drawing stage of a reverse draw operation asdisclosed in the Grigorenko patent, or instead, may be used solely forthe ironing operation.

In addition to the structural advantages and reduction in material andweight of the improved cylinder of the invention, additional advantagesare also realized. The cylinder material is precisely sized throughoutthe side-wall portion, affording a cylinder that is made to an exact,repeatable standard. By utilizing drawing and ironing techniques, suchas those disclosed in the Grigorenko patent, the drawn and ironed shellcan be produced in a single stroke operation of appropriate equipment,the drawn and ironed shell being ready for trimming. The sizing achievedby the ironing process also permits the virgin material employed to beof much less critical tolerance, thus increasing the availability (i.e.,source and acceptable tolerance) of the purchased raw, or virgin,material to be used. Since less material is employed, smaller initialdiscs are used as compared with conventional drawing operations,permitting better layouts in stamping the discs from sheets of virginmaterial and thus improving the yield of useable discs from a givensheet of material.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a process formanufacturing a cylindrical container includes the steps of drawing andironing, using a press, at least two metal shells, forming a containerusing the at least two metal shells, and attaching a valve portion tothe container via a brazing process.

In accordance with another aspect of the present invention, thecontainer has a sidewall, the sidewall having a thickness, the processfurther including the step of specifying the thickness of the sidewallto withstand hydrostatic pressure.

In accordance with another aspect of the present invention, the processfurther includes the step of maintaining a substantially consistentthickness via a substantially uniform clearance between a punch andironing ring.

In accordance with another aspect of the present invention, drawing andironing, using a press, at least two metal shells further includes thestep of drawing and ironing, using a hydraulic press, at least two metalshells.

In accordance with another aspect of the present invention, drawing andironing, using a press, at least two metal shells further includes thestep of drawing and ironing, using a mechanical press, at least twometal shells In accordance with another aspect of the present invention,the method further includes the step of attaching a base to thecontainer.

In accordance with another aspect of the present invention, the processfurther includes the step of increasing the thickness with each runthrough of the process.

Still other benefits and advantages of the invention will becomeapparent to those skilled in the art to which it pertains upon a readingand understanding of the following detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, at least one embodiment of which will be described in detail inthis specification and illustrated in the accompanying drawings whichform a part hereof and herein:

FIG. 1 is a top view of the inventive container;

FIG. 2 is a perspective view of the container;

FIG. 3 is a top view of the prior art container;

FIG. 4 is a perspective view of the prior art container;

FIG. 5 is an exploded view of Section A of FIG. 6;

FIG. 6 is a view of the inventive container in an ironing die;

FIG. 7 is a top view of another prior art container; and, FIG. 8 is aperspective view of the prior art container shown in FIG. 7.

DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes ofillustrating at least one embodiment of the invention only and not forpurposes of limiting the same, FIGS. 1 and 2 illustrate the inventivecontainer 10, which includes a valve portion 12, a valve 18, a body 14,and a base 16. FIGS. 3, 4, 7, and 8 show the prior art container 20,which has a top piece 26, a bottom piece 24, a base 36, a scuffprotector 22, and flanges 28. The flanges 28 are attached to the toppiece 26 and aid in the attachment of the top and bottom pieces 26, 24.The structure and operation of a cylindrical container are well known inthe art, and for the sake of brevity, will not be further discussedherein. Utilizing the drawing and ironing process described above, twohalf shells (not shown) are joined together to form the container 10. Abrazed, or similarly attached, valve portion 12 is attached to thecontainer 10. The container 10 is trimmed with a spin trimmer (a spintrimmer is a rotary trimmer used to trim the ends of tubular orcylindrical parts). The base 16 is connected to the bottom of thecontainer 10. This inventive process allows the sidewalls of the body 14to be thinner. This process also eliminates at least one part and atleast one assembly point, and can be used on any tubular part. In thisparticular embodiment, the base 16 is between approximately 0.045 inchand approximately 0.055 inch. This thicker base 16 enables the presentinvention to eliminate the need for an additional part to protectagainst scuffing the base 16. Since the additional part is eliminated,the manufacture and assembly process is made quicker, more efficient,and less expensive.

The inventive process, which utilizes a clearance between the punch andthe ironing ring, enables the correct size for the container 10 everytime. The brazing process helps relieve stress on the part. The brazingprocess is typically performed in either a batch, or conveyor type,furnace. Brazing, unlike welding, does not melt the parts together.Brazing is similar to soldering, except at a much higher temperature.Brazing uses brass or copper with a flux material for cleaning and flow.The result is that brazing is a much stronger joint than soldering. Ingeneral, the higher the melt temperature of the medium, the stronger thejoint. In this particular embodiment, the elimination of the scuffprotector 22 means one less part to manufacture and assemble, whichwould help realize a cost advantage without reducing any performancecharacteristics.

With reference now to FIGS. 5 and 6, part of the ironing process isshown. FIG. 5 is an exploded view of Section A of FIG. 6. FIGS. 5 and 6show the container 10, the base 16, an ironing ring 30, originalmaterial thickness 32, gap 38, and sidewall thickness 34. The gap 38between the ironing ring 30 and the container 10 controls the thicknessof the sidewall 34. This control aids in the container performance. Ifthe ring 30 begins to wear, the container 10 will be too short and willcause a failure to produce the desired length. Conversely, if the gap 38is too small, the container will be too long, which will also cause afailure. Therefore, the use of the drawing and ironing process enables amore accurately produced part. The ironing process changes the grainstructure (cold flow or forming), increasing the hardness (mechanically)that allows the process to perform effectively in this particularembodiment.

It is to be understood that this invention can be used on anycylindrical container, as long as chosen sound engineering judgment. Forexample, the present invention is applicable to fire extinguishers,medical grade Freon containers, and other pressurized andnon-pressurized cylinders. The previous list is not intended to belimiting or all-encompassing of the examples of the invention.

The invention has been described with reference to at least oneembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations in so far asthey come within the scope of the appended claims or the equivalencethereof.

Having thus described the invention, it is now claimed:

1. A process for manufacturing a cylindrical container, the processcomprising the steps of: drawing and ironing, using a press, at leasttwo metal shells; forming the container using the at least two metalshells; and, attaching a valve portion to the container via a brazingprocess.
 2. The process of claim 1, wherein the container has asidewall, the sidewall having a thickness, the process further comprisesthe step of: specifying the thickness of the sidewall to withstandhydrostatic pressure.
 3. The process of claim 2, wherein the processfurther comprising the step of: maintaining a substantially consistentthickness via a substantially uniform clearance between the containerand an ironing ring.
 4. The process of claim 1, wherein drawing andironing, using a press, at least two metal shells further comprises thestep of: drawing and ironing, using a hydraulic press, at least twometal shells.
 5. The process of claim 1, wherein drawing and ironing,using a press, at least two metal shells further comprises the step of:drawing and ironing, using a mechanical press, at least two metalshells.
 6. The process of claim 3, wherein the method further comprisesthe step of: attaching a base to the container.
 7. The process of claim6, wherein the process further comprises the step of: increasing thethickness with each run through the process.
 8. The process of claim 7,wherein the container is a cylindrical container.
 9. A cylindricalcontainer, the container comprising: a body, the body being formed by adrawing and ironing process; and, a valve portion, the valve portionbeing attached to the body via a brazing process.
 10. The container ofclaim 9, wherein the body has a thickness, the thickness being enough towithstand hydrostatic pressure.
 11. The container of claim 10, whereinthe container further comprises a base, the base attached to the bottomof the container.
 12. The container of claim 11, wherein the containeris a cylindrical container.
 13. A cylindrical container made inaccordance with the process of claim 1.